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Abstract

We report a large-area, semi-transparent, light-sensitive nanocrystal skin (LS-NS) platform consisting of single monolayer colloidal nanocrystals. LS-NS devices, which were fabricated over areas up to 48 cm2 using spray-coating and several cm-squares using dip-coating, are operated on the principle of photogenerated potential buildup, unlike the conventional charge collection. Implementing proof-of-concept devices using CdTe nanocrystals with ligand removal, we observed a substantial sensitivity enhancement factor of ~73%, accompanied with a 3-fold faster response time (<100 ms). With fully sealed nanocrystal monolayers, LS-NS is found to be highly stable under ambient conditions, promising for low-cost large-area UV/visible sensing in windows and facades of smart buildings.

Effect of photocharge trapping inside the NCs as the incident light shines continuously on the nanocrystals skin for different periods of time at 350 nm (0.175 mW/cm2). Here the total of incident optical energy given in the legend is the amount of incident optical power multiplied by the exposure time and the exposure area.

(a) Variation of the voltage buildup at different excitation wavelengths and intensity levels. Light was turned off after reaching the peak point. (b) Corresponding sensitivity curve of the LS-NS device as a function of excitation wavelengths.

(a) Response time increases with the decreasing power since both deeper and shallower states saturate and (b) increasing illumination, resulting in decreased sensitivity because of filling the long-lived trap states. Arrows indicate the point in time when the light was turned off.

(a) Variation of voltage buildup with time for 0.175 mW/cm2 at 350 nm and (b) RC decay change in time by turning the incident light on and off for 0.153 mW/cm2 at 350 nm wavelength in the case of ligand-removed LS-NS devices.